1. Field of the Invention
The present invention relates to a hydraulic tensioner device for applying appropriate tension to an endless transmission member, such as an endless chain or an endless belt, which transmits driving force of a valve train of an internal combustion engine.
2. Description of Related Art
A hydraulic tensioner device for tightening looseness in an endless transmission belt that transmits power to a rotary shaft of a valve train from a rotary shaft of an internal combustion engine includes as separate parts: a pressure maintenance valve for maintaining, at a constant level, hydraulic pressure generated inside a hydraulic chamber of a tensioner body, which is pushed in by counteraction to application of tension on the endless transmission belt; and an air release valve for releasing air generated inside the hydraulic chamber (see Japanese Patent Application Publication No. 2012-211643).
In the hydraulic tensioner device described in Japanese Patent Application Publication No. 2012-211643, appropriate tension can be applied to the endless transmission belt since the pressure maintenance valve maintains hydraulic pressure inside the hydraulic chamber of the tensioner body at a constant level, and excessive tension is not applied to the endless transmission belt since the air release valve allows air contained in the oil inside the hydraulic chamber of the tensioner body to be separated from the oil and released into the atmosphere.
However, providing a pressure maintenance valve and an air release valve as separate parts in a hydraulic tensioner device not only complicates the structure and increase the number of parts, but also enlarges the hydraulic tensioner device in size and inevitably increase manufacturing cost.